Optimization of Magnetic Coating for Improved Electromagnetic Wave Absorption in Bi-Layered Nano-Hollow Spheres

A thorough search for effective microwave absorption materials (MAMs) has recently drawn a lot of interest to combat the increasingly serious electromagnetic (EM) pollution. Here, it is studied that coating MnFe2O4 (MnFO) nano-hollow spheres (NHS) with a layer of CoFe2O4 (CFO) of optimized thickness and high magnetic permeability performs efficiently to attenuate EM waves for a greater reflection loss (RL) at a thinner absorber thickness over a wide frequency range. Superior absorption qualities of MnFO NHS are caused by a larger interfacial area, greater magnetic anisotropy, internal reflections and scattering from NHS, as well as a higher magnetic permeability of MnFO. With a composite absorber of only 4.46 mm thickness and a filler concentration of 20%, the MnFO (diameter ~450 nm and shell ~50 nm) at CFO (thickness ~35 nm) bi-layered NHS achieves a high RL of −66.48 dB. We can indeed optimize for better absorption with a minimal composite absorber thickness according to the aforementioned investigation on the variation of CFO thickness over MnFO NHSs. This work reveals the very promising low-cost, lightweight, and optimized MnFO@CFO NHS as a viable EM wave absorber for high-frequency applications.